This invention relates generally to a manifold calibration finger for use with a die head in the extrusion of a plastic, and more particularly to an improved structure capable of forming a pipe wall with apertures therein when the pipe is examined in cross-section.
Plastic pipe has found a variety of uses especially relating to drainage. One of the concerns in the manufacture of plastic pipe is the amount of raw materials consumed and the resultant weight of the finished product. For example, 48" interior diameter solid wall plastic pipe weighs approximately 200 lbs per foot. It has recently been discovered that plastic pipe having apertures formed therein, when the pipe is viewed in cross-section, weighs approximately 30 lbs per linear foot. However, a problem exists in designing a machine capable of manufacturing pipe having the desired cross- section.
In general, extruded plastic pipe is formed on a production line having a variety of specific machines incorporated into the manufacturing process. One of the first machines is an extruder. Plastic powder, or more preferably pellets, is fed through the extruder where it is subjected to high temperatures such that the plastic melts. The plasticized plastic then proceeds through a feed tube, at the end of which the plastic enters into a typically drum shaped die. At the front of the die is the specific cross-section profile to be extruded. As the hot plastic comes out of the die, it passes over what are called calibrating or calibration fingers which assist in maintaining the desired cross-sectional form which has been extruded. In addition to the extruder and die, which is supported on a die post assembly, plastic pipe is manufactured using a former or forming head.
Prior art manifold calibration fingers have apparently limited the ability to manufacture a plastic product having the cross-section which incorporates apertures. It is thus apparent that the need exists for an improved manifold calibration finger which manufactures a product having the desired cross-section.